The present invention is in an absorbent body of nonwoven material with hydrophilic or oleophilic fibers of 1 to 50 mm length, and a method for the production thereof. The absorbent body of the invention has medical, hygenic and technical applications where it is a component of liquid-absorbing products, such as surgical absorbent cloths, products for the absorption of physiological liquids such a diapers, incontinence pads, tampons and sanitary napkins, or highly absorbent wiping cloths as well as automative oil filters.
A layer of shredded, air-deposited cellulose is usually used as hydrophilic absorbent material. The hydrophilic material may be mixed with synthetic fibers.
Known generic absorbent bodies have considerable shortcomings. The absorbed liquid is deposited in the interstices between the loosely laid staple fibers. Under stress, e.g., under the weight or movement of the wearer of a diaper, this liquid easily escapes again as if squeezed from a sponge. Also, due to poor consistency, mats of short cellulose fibers easily fray by creasing and rubbing (wearing of diapers) thereby losing their capillarity and thus their ability to carry the absorbed liquids. Since cellulose fibers are short (1 to 50 mm) and loosely laid to achieve a greater capacity for the absorption of liquid, their capillary function is also inadequate. In other words the transport of liquid into the fiber interstices is imperfect. Consequently far less liquid advances within the absorbent body than the latter would theoretically be able to absorb.
Another drawback of such a product is that its bulk diminishes when it is full of liquid, that is to say that its fluff collapses, its absorption capacity is drastically reduced, and liquid leaks out.
It is possible to increase the capillarity and also the wet strength of an absorbent body by creating a more dense arrangement of the cellulose fibers. This, however, drastically reduces the volume that is available for the absorbed liquid, which is aggravated by the above-described reduction of the absorptive capacity for moisture in the liquid-filled state. If as a remedy the quantity of fiber is multiplied (e.g., several layers of absorbent material), an excessively thick and heavy product is formed, resulting in a considerable increase in material costs and unreasonable handling difficulties. In the case of incontinence inserts, the thickened product is uncomfortable to wear.
There have been many attempts to find a solution to the dilemma of providing absorbent bodies with a high and lasting capacity for absorbing liquids (high bulk, virtually no capillary function) while attempting to increase the distribution of liquid between the fibers via a greater fiber density.
European Patent A 108 637 teaches combining both types of nonwoven material and creating a compressed composite consisting of a thin, highly compressed fiber mat as liquid distributor, plus a loosely laid fiber mat of low density for the storage of the liquid. The dense fiber mat contains hydrophilic fibers and is backed with a lightly compressed fiber layer which contains superabsorbent polymers (swelling bodies, superabsorbers). Such polymers are water-insoluble, hydrophilic polymers which can absorb at least 15 times their weight of water. They are used in the form of powders, flakes or granules.
The light pressing of the superabsorber particles between two layers of fiber, plus, in some cases, fixation with adhesives, binding agents or by embossing, is intended to fix the particles in a uniform distribution to prevent their leakage in the dry state and, to prevent them, in the presence of moisture, from conglomerating due to the lack of sufficient separation thus interfering with the liquid distribution.
The disadvantage of such fixation is that the particles have a very limited amount of space available to swell into. As such, their ability to absorb liquids is considerably impaired.
Furthermore, an absorbent body according to the above patent has good liquid distribution in the high-density fiber layer, yet transport into the actual storage layer is disturbed since there is no direct contact between the transporting layer and the superabsorber particles; the outer surface of the layer fixing these particles acts as a barrier to liquids.
Also, in the wet state the composite easily separates and becomes lumpy.
Composites, finally, are always relatively stiff and inelastic and so they are uncomfortable to wear in incontinence products. Their production requires several separate steps.